Until fairly recently, the cable network was predominantly a vehicle for delivering entertainment. With the advent of the Internet and the rise in demand for broadband two-way access, the cable industry began to seek new ways of utilizing its existing plant. Pure coaxial (“coax”) cable networks were replaced with hybrid fiber networks (HFNs) using optical fiber from the head end to the demarcation with the subscriber coax (usually at a fiber node). Currently, a content-based network, a non-limiting example of which is a cable television network, may afford access to a variety of services besides television, for example, broadband Internet access, telephone service, and the like.
One significant issue for a cable operator desiring to provide digital service is the configuration of its network. Designed for one-way delivery of broadcast signals, the existing cable network topology was optimized for downstream (toward the subscriber) only service. New equipment had to be added to the network to provide two-way communication. To reduce the cost of this equipment and to simplify the upgrade of the broadcast cable for two-way digital traffic, standards were developed for a variety of new cable-based services. The first of these standards, the Data Over Cable System Interface Standard (DOCSIS® standard), was released in 1998. DOCSIS® establishes standards for cable modems and supporting equipment. DOCSIS® (Data Over Cable Service Interface Specification) is a registered mark of Cable Television Laboratories, Inc., 400 Centennial Parkway Louisville Colo. 80027, USA, and will be referred to for the remainder of this application in capital letters, without the ® symbol, for convenience.
IP addresses are allocated in blocks known as subnets or prefixes on a network. These addresses are regularly allocated and moved as part of network growth and expansion. A cable modem termination system or CMTS is a piece of equipment typically located in a cable company's head end or hub site, and used to provide high speed data services, such as cable Internet or voice over Internet Protocol (VoIP), to cable subscribers. A CMTS provides many of the same functions provided by the digital subscriber line access multiplexer (DSLAM) in a digital subscriber line (DSL) system.
On a DOCSIS network, IP subnets are allocated on a per-CMTS basis.
The Dynamic Host Configuration Protocol (DHCP) is a network protocol that is used to configure network devices so that they can communicate on an IP network. A DHCP client uses the DHCP protocol to acquire configuration information, such as an IP address, a default route and one or more DNS (domain name system) server addresses from a DHCP server. The DHCP client then uses this information to configure its host. Once the configuration process is complete, the host is able to communicate on the internet.
The DHCP server maintains a database of available IP addresses and configuration information. When it receives a request from a client, the DHCP server determines the network to which the DHCP client is connected, and then allocates an IP address or prefix that is appropriate for the client, and sends configuration information appropriate for that client.
Enterprise DHCP servers are commonly deployed in a cluster configuration where a pair of servers share responsibility for providing leases to a defined set of network infrastructure. In a cable network, a DHCP cluster is responsible for providing DHCP leases to clients configured on a set of CMTSs. Each CMTS is configured with the IP addresses of the two DHCP servers and the servers are configured with the IP address ranges available on the CMTS. A DHCP cluster serves multiple CMTSs, typically grouped by geographic area.
There are many types of IP networks besides cable networks. Other wired IP networks include, for example, digital subscriber line (DSL), fiber to the home, fiber to the curb, and so on. Wireless IP networks include Wi-Fi, wireless ISP (Internet Service Provider), WiMAX, satellite internet, and mobile broadband.